This invention relates to a method of forming a bead for a pneumatic tire and, more particularly, to a method of forming a bead where the trailing end of at least one bead wire is anchored in the bead.
The beads of a pneumatic tire are composed of high tensile steel wire formed into inextensible hoops. The bead functions to anchor the plies of the tire and to hold the tire to the rim of a wheel.
In the manufacture of a tire bead, the bead wire is generally coated with rubber. A leading end of the rubber coated bead wire is secured by a gripping mechanism which is part of a collapsible, ratable bead former. The former is rotated and the rubber coated bead wire is wound around the former a plurality of revolutions. The rubber coating on the wire is uncured so that each revolution of wire adheres to the previously wound revolutions. When the desired cross-sectional shape of the bead is formed, the bead wire is cut to form a trailing end. The trailing end is adhered to the previous revolutions, the former is collapsed, and the bead is removed from the former.
When the bead is built into a pneumatic tire, spring back of the bead wire can occur. During the curing process, the rubber surrounding the bead wire liquefies, reducing its adhesiveness. As the adhesiveness of the rubber is reduced, the bead wire may attempt to spring back to its original shape. This spring back causes the trading end of the bead wire to pull away from the rest of the bead and protrude radially outwardly into the tire. One technique for preventing spring back of the trailing end 12 of the bead wire 14 is to wrap the bead 10, shown in FIG. 1 and FIG. 2. After forming the bead 10, it is placed on a separate machine and is wrapped with a plurality of nylon cords 30, or a like substitute, at intervals around its circumference. The cords 30 keep the trailing end 12 of the bead wire 14 in place during the curing process. Although wrapping the bead 10 eliminates spring back of the trailing end 12 of the bead wire 14, the wrapping process increases labor and material costs associated with the manufacture of beads 10.
Another technique for preventing spring back of the trailing end of the bead wire is to anchor the trailing end within the body of the bead. U.S. Pat. No. 4,938,437 provides a method of manufacturing rubberless single wire tire bead assemblies having at least one end positioned internal to the array of wires comprising the body of the tire bead assembly. This method places all the revolutions of the bead wire on a special former having movable parts and uses the moveable parts to slide the respective revolutions of bead wire into a position surrounding the wire end. This method is limited to rubberless bead wires so the adhesive forces of the uncured rubber coating is not a factor in performing the method.
This invention provides a method of forming a bead 10 where the trailing end 12 of at least one bead wire 14 is anchored in the bead 10. The method including the steps of: securing a leading end of the bead wire 14; winding the bead wire 14 about a former 42 a plurality of revolutions to form the bead 10 into the desired cross-sectional shape; and cutting the bead wire 14 after a last revolution 28 about the former 42.
The method is characterized by the step of: anchoring the trailing end 12 of the bead wire 14 by driving the trailing end 12 into the bead 10. The driving of the trailing end 12 forces the trailing end 12 between at least two previously wound, abutting revolutions of the bead wire 14, at least temporarily separating the respective revolutions.
The method of this invention can be performed using either a rubberless or a rubber coated bead wire.
For ease of understanding this disclosure, the following terms are disclosed. xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards, and chafers, to fit the design rim. The beads are associated with holding the tire to the wheel rum so that the driving and baking forces are transmitted from the vehicle to the ground. xe2x80x9cPneumatic tirexe2x80x9d means a laminated mechanical device of generally toroiddal shape, usually an open torus, having beads and a tread and made of rubber, chemicals, fabric and steel or other materials. When mounted on the wheel of a motor vehicle, the tire through its tread provides traction and contains the fluid that sustains the vehicle load. xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d are used to mean directions toward or away from the axis of rotation of the tire.